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Патент USA US3036235

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May 22, 1962
Filed May 1, 1959
2 Sheets-Sheet 1
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May 22, 1962
Filed May 1, 1959
2 Sheets-Sheet 2
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Patented May 22, 1962
thereafter causes the reverse breakdown of the second
Solomon L. Miller, Poughkeepsie, N.Y., assignor to Inter
national Business Machines Corporation, New York,
N.Y., a corporation of New York
Filed May 1, 1959, Ser. No. 810,371
8 Claims. (Cl. 307-885)
In accordance with another embodiment of the inven
tion, there is an electrical circuit functioning as a diode
with a negative resistance characteristic which consists
of two semi-conductor devices, one having ‘a junction with
a critical reverse breakdown voltage and the other having
a junction with a constant voltage characteristic in its
forward direction, and connected together by external
This invention relates to negative resistance electrical
impedance means across which a potential drop appears.
circuits which employ two semi-conductor devices, which
occasioned by increased current ?ow due to the reverse
circuits exhibit the so-called hook characteristic. The
breakdown of one junction and which thereafter causes
invention operates in accordance with similar principles
the other junction to conduct heavily .in its forward
disclosed in the copending US. application, Serial No.
780,300, ?led by Richard Rutz, on December 15, 1958,
In the drawings:
and assigned to the assignee of the instant application.
FIGURE 1 is a diagrammatic representation of a circuit '
In the conventional hook collector semi-conductors in
including a conventional PNPN diode;
the prior art of the type described in “PNPN Transistor
FIGURE 2 is a graphical illustration of voltage versus
Switches” by J. L. Moll et al., Proc. IRE. vol. 44, Septem
current under the conditions of operation of a negative
ber, 1956, the voltage at which the critical junction of
resistance structure illustrating both the present invention
the semi-conductor breaks down to provide a rapidly 20 and the prior art;
increasing current through the transistor is well-de?ned.
FIGURE 3 is an analytic illustration conventionally
However, not so well de?ned is the current through the
transistor at which the negative resistance characteristic
used to explain the functioning of a device such as
is evidenced. Consequently, in the conventional type of 25 FIGURE 4 is a diagrammatic illustration of a negative
resistance device constructed in accordance with the in
the point at which the voltage switches from the critical
vention of the aforementioned U.S. application Serial No.
breakdown voltage ‘across the transistor to a minimum
780,300, and employed in a circuit which will exemplify
voltage thereacross. Also, the current in this switching
its functioning;
region is an irregular function of the voltage. Further, 30 FIGURE 5 is a diagrammatic illustration of one em
capacitive currents and variations in alpha of different
bodiment of a negative resistance electrical circuit con
portions of the prior art devices contribute to a response
structed in accordance with the present invention.
behavior which is different for different switching rates.
FIGURE 6 is a diagrammatic illustration of another
In the above—mentioned US. application Serial No.
embodiment of a negative resistance circuit constructed
780,300 is disclosed a single unit multiple junction semi 35 in accordance with the present invention.
hook transistor in the prior art there is little control over
conductor device functioning as a diode in which hook
FIGURE 7 is a graph representing a set of character
istic I—V curves for a two-terminal, forward biased,
of at least two of said junctions so that the critical voltage
constant potential, breakdown device as utilized in the
at which the ?rst junction breaks down de?nes the initia~
embodiment of this invention shown in FIGURE 6‘
tion of high current, and the ?ow of high current in turn 40' In the accompanying drawings FIGURES'I to 4, in
action is achieved by the avalanche voltage breakdown
?owing through the selected internal resistance in one
zone produces a voltage drop which causes the break
down of a second junction and initiates hook action,
which thus manifests the negative resistance character
clusive, are taken from the previously identi?ed copend
ing application.
Referring ?rst to FIGURES 1 to 3, inclusive, the
diode 10 is a PNPN diode constructed in accordance
istic of the device. By the term “hook action” is meant
with the prior art. It is connected in series with a re
that the total ampli?cation factor of the device becomes
sistor 11 to the plus side of a variable voltage source
greater than or equal to unity. In this device the break
12. The negative side of the source '12 is connected to
down voltage of the second junction is lower than the
the outermost N-region of the diode 10 and both are
breakdown voltage of the ?rst junction, and there is an
jointly connected to ground. Referring to FIGURE 3,
appreciable resistance built into the device. The term
50 there is shown a diagrammatic illustration of the func
“avalanche” is employed to include both avalanche or
tioning of the diode of FIGURE 1. Actually, the diode
Zener mechanisms currently used in the art and any
of FIGURE 1 acts in the circuit'in a manner similar
voltage sensitive similar breakdown mechanism.
to the PNP and NPN transistors arranged in the man~
It is therefore an object of this invention to provide
ner shown in FIGURE 3. The P-region >13 of diode
negative resistance electrical circuits employing semi
10 is the same as the P-region 17 of transistor 23; the
conductor devices in which the breakdown voltages of
N-region 14 is the same as the N-regions 18 and 19
two junctions are well de?ned whereupon the current
of transistors 23 and 24; the P-region 15 is the same
flowing through the electrical circuit rapidly increases.
as the P-regions 20 and 2.1 of the transistors 23 and 24,
It is another object of this invention to provide nega
and the N-region 16 is the same as the N-region 22 of
tive resistance electrical circuits in which the value of
transistor 24. The load resistor 11 is common in both
current ?owing through the circuit during the manifesta 60 of these diagrams, as is the variable voltage source 12.
tion of negative resistance is well de?ned.
Another object is to provide a controllable negative
resistance characteristic for a four-zone transistor.
In accordance with one embodiment of the invention
there is ‘an electrical circuit functioning as a ‘diode with
a negative resistance characteristic which consists of two
semi-conductor devices, each having a junction with a
critical reverse breakdown voltage and connected to
gether by external impedance means across which a po
Upon the application of a relatively small voltage to the
transistors 23 and 24, the PN diode of transistor 23
is forward biased. However, the NP diodes 18 and 21
of transistor 23 and the NP diodes 19 and 20 of tran
sistor 24 are reverse biased. Consequently, the only
current ?owing therethrough is essentially the ICD of t ese
diodes which is the reverse leakage current therethrough
of an extremely small value. As the voltage applied
across the transistors increases this saturation current
tential drop appears occasioned ‘by increased current ?ow 70 increases somewhat until ?nally both junctions de?ned
due to the reverse breakdown of one junction and which
between the NP diodes of transistors 23 and 24 break
between points A2 and B2 in the N-region 4 due to the
current ?owing in path 38. This is because the P-region
33 is more lightly doped than ‘is the N-region 4, and thus
At this time an increased amount of current
is permitted to ?ow therethrough and the transistors in
e?fect offer a greatly decreased impedance to current
?ow. When this happens the transistors combine to
provide a negative resistance characteristic by virtue of
the fact that the large current ?ow is accompanied by
a decrease of voltage droprthereacross. The point at
provides more resistance to the ?ow of current. This
difference in resistance can be further insured by mak
ing the N+ region 34 thin and covering it with a good
conductor such as a solder coating not shown. This po
tential drop, then, between points A1 and B1 in the P
which the breakdown occurs is a function of the voltage
applied across the transistor which reaches a critical value
'whenthe two NP diodes in the transistors 23 and 24
break down. The current rapidly increases to a stable
value accompanied by a reduction in voltageacross these
two transistors. The current value at which this negative
region 33 is of such a magnitude so as to cause the right
hand section of ‘P-region 33 to be at a lower potential
than is the right-hand section of N-region 34, thus creat
ing a reverse bias at this section of the J3 junction. Since
' the N+ region is of very low resistance, it may be con
sidered to be equipotential throughout and point 39 is a
resistance characteristic is initiated is not well de?ned and
also current in this critical region is an irregular func 15 point along the junction J3 and the region 33 where the po
tion of the’ voltages.
tential is equal to the’ potential of region 34; The device
is further doped such that the reverse breakdown voltage
for junction J2 will be much greater than the reverse
The operation of these two transistors 23 and 24 ex
emplifying the operation of a typical negative resistance
breakdown voltage for the right-hand section of junc
device such as the diode it} of FIGURE 1 is shown
graphically by dotted line in FIGURE 2. As can be 20 tion 13.
For- applied voltages Vn across the semi-conductor
seen, as the voltage increases across the transistor there.
device which are less than the breakdown voltage for the
is initially a very small increase in the current ?ow’
junction 12, only small reverse currents will ?ow across
therethrough as represented by the portion of the curve.
this junction and through parallel paths 37 and 38 to
labeled 25. However, when V1 is reached, the cur
rent has reached a value which will cause breakdown of 25 the base ohmic connection 36. The current through the
essentially equipotential N-region 34 will be quite limited
the critical junction in the diode It}. At' a certain cur
by the low reverse leakage current coming through the
rent, de?ned by the fact that the sum of the low voltage
reversed bias section of junction 13. Point A on the
alpha of the individual portions of the device exceeds
curve 25 shown in FIGURE 2 will be reached when the
unity, the’hook action is initiated. The voltage across
the‘diode 1t) collapses with'an increase of current there 30 applied voltage *V,, equals the breakdown voltage for
junction I2, which corresponds to V1 on the curve. Thus
through denoted by the portion of the move labeled 27,
junction J2, whose resistance has been decreased due
to the avalanche breakdown phenomenon occurring at
thusrnanifesting the negative resistance characteristic.
:The negative resistance circuit constructed in accord
ance with thisv invention, however, willfunction as illus
trated by the solid'lined curve including indicative por
tions labeled 25 and 26 which describes the sheet. The
' voltage V1, will permit a higher current to flow into the
bottom two P-N regions. This current is represented
by the line 26 in FIGURE 2. The greater portion of
this higher current will flow in path 37 of P-region 33
and will increase the potential drop between P-region 33
initial portion of the solid curve is substantially identical
to the initial portion ‘of the dotted curve.’ Here it can be >
seen that the current values at which the hook action B, ' and N-region 34 at the right-hand section of junction 13.
as well as the avalanche action A, are initiated are well 40 When the drop across the right-hand section of junction
J3 reaches the breakdown voltage of J3, then a large
defined; The current at the hook action Bis identified as
current begins to ?ow in path 33 through the N-region 34.
I2. ''Also the current flow through the‘negative resistance
The breakdown of junction 1371's considered to occur at '
circuit constructed in accordance with this invention dur
ing the collapse of voltage from Y1 and V2 across the cir
point B shown in the curve ‘in FIGURE 2. Thus, at
point B of FIGURE 2 there are now two large currents
?owing in paths 37 and 38 of FIGURE 4. The sum
cuit is ‘a more linear function of this voltage than is indi
cated by the portion 21 of the dotted curve. '
of these two currents must equal the current ?owing‘
across junction J2. It is therefore seen that‘ the. e?ective
resistance of the parallel pathsj37 and 38 is reduced when
_ For the purpose of‘inerely outlining. the ‘basic principle
of two-junction breakdown which is employed in, the
present invention, FIGURE 4 is now‘ referred to which
shows an embodiment of the invention disclosed inthe 50 the voltage breakdown at the right-hand section of I3
is reached.
aforementioned US. application Serial No. 780,300.
The variation in curvature at point A in the curve is
The negativeresistance device is four-region PNPN semi- .
due to the fact that the avalanche process ca'n'be sus
conductor structure,rand in this illustration the two ter
tained ‘at a slightly lower voltage due to an increase in
minal ohmic connections 35 and 36 are now made to P
re’gio'ns 21 and 33, respectively, while the N-regions 32
and>34 are left ?oating. As may beapparent to one skilled
in the art, connections to the ?oating regions may be made
for signal introduction purposes. P-regions 3-1 and N
injection oivholes from the P+ region 31 as current
increases. This process, in general, is the beginning of a
negative resistance such asycurve 27 of the prior art,
however, in the device shown in ‘FIGURE 4 the built-in
positive resistance in region 33 over-rides the negative
regions 34 are more heavily doped with their respective‘
impurities than are the two innermost -N andPéregions 60 resistance and provides a" positive ‘slope 26 to the portion
32' and 33, respectively. A region heavily doped pro- ~ ' of ‘the curve between'po'ints A and B. In cases where
vides less’ resistance to current passing therethrough than
the injection of junction J1 is constant the voltage indi
- does a region lightly doped.
If a positive’ potential is applied to the top P-reglon
31_ as shown in FIGURE '4, then the three 'PN junctions. 65
cated asVb will equal V2 and the slope of the portion 26
of the curve will be a measure .of the effective resistance
of zone 33.
labeled ‘J11 and J2; andrl3 will be ibias'edr' as. indicated.
The large current coming out of the forward biased
vJunction I1’ is biased in a t rward direction since a more
region'of junction 13' will be minority carriers so that it
positive voltage'is applied to the P-re‘gion 31. than is ap
acts as the? emitter to the hook collector formed by
'' iplied ‘to 'theejNsregionbz. Conversely; junction '12 is
.P-region 31 and N-region 32." This large ‘current, which‘
reversed biased, sinceN-regionSZ is at a more positive
is indicated at point B o'f-FIGURE 2, now causes the
potential than is P-region 33. Junction J3, however, will j voltage across the entire unit togcollapse to voltage V2
be‘both forward and reversed biased indifferent places as.
'due to typical hook collector transistor action. .A negative
. shown. This is due tothe fact the potential drop from
resistance’characteristic is thus. exhibited bythe device.
point Alito point 131 in P-region 33 due tothe current" Since the. only function of the P~region 31 and N-r'egion‘:
. ?owing in path 37‘will. be ‘greater than the potential drop 75 32 is to provide a PN hook collector, it is seen. that
top junction J1 may be replaced by any electrode with
responds to the reverse biased right-hand portion of junc
tion Is in FIGURE 4.
Diode 40 may be an ordinary multiple junction PNPN
an inherent amplifying and multiplying action.
In summing up the above operation, it is seen that
more current to ?ow in path 37 of P-region 33 than was
crystal which exhibits a negative resistance characteristic
due to the PN hook collector formed by P-region 41 and
N-region 42'. The critical breakdown voltage across
formerly ?owing before voltage V1 was reached. This
junction I2 is chosen to be fairly large and corresponds
at point A of the curve shown in FIGURE 2 the break
down voltage V1 of junction J2 is reached, thus causing
to the breakdown voltage across junction J2 of the diode
the right-hand section of junction I3 to become greater
shown in FIGURE 4. The Zener diode 47 is selected
until the breakdown voltage of junction I3 is attained, 10 for a low critical breakdown voltage across its junction
J4, and this breakdown voltage corresponds to that neces
at which time point B has been reached on the curve
sary across the right-hand section of junction J3 in FIG
of FIGURE 2. Upon the breaking down of the junc
URE 4. The impedance 55 performs the function of
tion 13 a large current can now begin to ?ow in path
the lateral impedance which is built into the base P-region
38 as well as in path 37, thus creating a much larger
current ?ow through the entire device and especially 15 33 of the (‘diode in FIGURE 4. That is, it is the means
for creating a reverse bias potential on junction J4.
through junctions J2 and J1. The typical hook action of
In operation, the circuit shown in FIGURE 5 works
the top PN hook collector now occurs wherein, since
in a similar fashion as was explained in connect-ion with
region 34 is established by the broken down portion of
FIGURE 4. The current ?owing across junction J2 of
1;; at essentially reference potential, any increase in ?ow
increased current in path 37 causes the reverse bias on
through path 37 serves to increase the forward bias on 20 diode 40 divides into two paths 55 :and 56.
the forward biased portion of J3 and therefore in
creases the injection of minority carriers each of which
While the
back resistance of junction Jr of diode 47 remains high,
the current ?owing in path 56 remains negligible. Junc~
tion 1;, of diode 40 is forward biased, but the voltage
liberates Os majority carriers where 0: is the ampli?ca
drop in impedance 55 due to current ?owing therethrough
tion of the hook. The entire voltage across the device
25 creates a reversed bias condition at junction 1., in diode 47
thus reverts to voltage V2 as is shown in FIGURE 2.
due to the fact that N-regions ‘44 and 51 are essentially at
It is seen, therefore that the voltage breakdown of
an equipotenti'al condition. When the reverse breakdown
both junctions J2 and I3 is required before the PNPN
voltage of junction I2 is reached, as indicated at point
diode of FIGURE 4 exhibits a negative resistance char
A on curve 25 of FIGURE 2, the current through im
acteristic due to the action of its PN hook collector.
The critical breakdown voltage junction J2 is essentially 30 pedance 55 is measurably increased. This results in a
applied by voltage V,,, which is of large magnitude.
However, the voltage drop across the right-hand section
of junction 13 is created only by the current ?owing in
parallel paths 37 and 38. The magnitude of this volt
age drop is therefore somewhat limited, and so the criti- >
cal breakdown voltage across junction J3 at this point
must be low as compared to that for junction J2. Fur
thermore, the P-region 33 must be doped in such a
manner so as to provide a lateral impedance path there
through which is much greater than the impedance of a
path through N-region 34. The process of fabricating
such a single unit semi-conductor device must therefore
be closely controlled so that the above-described criteria
can be obtained.
In accordance with the present invention, an electrical
greater potential drop between P‘-regions 43 and 50 which
results in the breakdown voltage of junction 14 being
reached. ‘The breakdown at junction 1.; then reduces the
resistance of path 56 and allows a large current to flow
N-region 44 of diode 40 now acts as an
emitter for the PN hook collector formed by P-region
41 and N-region 42 of diode 40. The current ampli?ca
tion created by hook action causes the entire electrical
circuit to display a negative resistance characteristic, such
as exhibited by curve 26 beginning at point B in FIG
URE 2, and the voltage across ohmic connections 45
and 48 rapidly reverts to the value of V2.
FIGURE !6 shows another ‘embodiment of the electri
cal circuit of the present invention. This circuit is similar
45 to the one shown in FIGURE 5, with the exception that
circuit exhibiting negative resistance is constructed in
the polarity of Zener diode 47 is reversed, i.e., the N-region
which two ordinary semi-conductor devices are employed,
each having one of the tWo breakdown junctions neces~
sary for the operation according to the basic principles of
is connected to the N-region 44 of diode 40. Diode 47
the invention disclosed in the aforementioned applica
tion. FIGURE 5 shows one embodiment of the elec
trical circuit of the present invention. There is shown
a multiple junction single crystal PNPN diode 40 which
is connected in circuit with a single junction Zener diode
47. The positive side of a variable voltage Vn is con
nected to a base ohmic contact 45 at the P-region 41.
Two ohmic contacts 46 and 49 and lead 56 connect to
gether the N-regions 44 and 51 of diodes 40 and 47,
respectively. The impedance 55 is connected between
two ohmic contacts 52 and 48 which are attached to P
regions 43 and 50 of diodes 4t) and 47, respectively.
The negative side of voltage V1!, is connected to ohmic
contact 48 which is attached to P-region 50 of diode 47.
P and N-regions 41 and 42 of diode 40 correspond to
51 is now connected to resistance 5'5 while the P-region 50
is preferably chosen so as to have a constant voltage por
tion in its forward direction characteristic, typical operat
ing characteristics of which are shown in FIGURE 7
as disclosed in the Motorola, Inc. publication No. R163
printed in February 1959 and published March 1, 1959,
entitled, Diffused Junction Silicon Power Recti?ers. This
means that for small positive potentials across junction
J4, very little current will ?ow until a particular magnitude
of this positive potential has been reached, whereupon a
large current will begin to ?ow in the forward direction
through the diode while the voltage ‘across junction 14
thereafter remains substantially constant. In operation,
the circuit of FIGURE 6 performs in a manner similar to
that of FIGURE 5. Upon the reverse breakdown of junc
tion J2 in diode 40, the increased current flow through
resistance 55 will cause a larger potential drop to be
P and N-regions 31 and 32, respectively, of the diode 65 developed between the N and P-regions of diode 47, al
though very little current will ?ow therethrough until
shown in FIGURE 4. N-regions 44 and 511 of diodes 40
the magnitude of this potential drop has reached a particu
and 47, respectively, also correspond to the N-region 34
lar value depending upon the characteristic of diode 47.
of the diode in FIGURE 4, since they are essentially at
Upon such a magnitude being reached by a continued in
equipotenti-al. P-regions 43 and 50 of diodes 4t} and 47,
crease in current through resistance’ 55, a large forward
respectively, correspond to the left- "and right-hand por
current begins to ?ow through diode 47 which thus allows
tions, respectively, of P-region 33 in FIGURE 4. Junc
N-region 44 of ‘diode 40 to now act as an emitter for the
tions 11 and J2 of diode 40 also correspond to junctions
PN hook collector formed by P-region 41 and N-region
J1 and J2 in FIGURE 4. Junction is of ‘diode 40 corre
42. It will be noted that the value of the constant volt-age
sponds to the forward biased left-hand portion of junc
tion 13 in FIGURE 4, while junction L, of diode 47 cor 75 formed across diode 47 will usually be smaller than the
7 f‘
second magnitude is reached, and a pair of terminal means
selectively connected to the other end region of said ?rst‘
device and to said second region'of said second device
which are adapted to receive a variable biasing potential
therebetween, with said relatively high impedance means
reverse breakdown voltage required for this diode. How
ever, the operation of diode 47 ‘in FIGURE 6 is equivalent to its operation in FIGURE 5, since in both cases
there is a low current ?ow through diode 47 until a par
ticular potential has been developed across its junction by
being adjusted so as to cause said ?rst rectifying junction
virtue of the increased current ?ow through the resistance
in said ?rst device to breakdown in time prior to the
breakdown of said junction in said second ‘device in re
The current I2 at which point B in FIGURE 2 occurs
sponse to an increase in the value of a biasing potential
is governed by the following equation:
I2R(55)~=forward voltage on I3+voltage on L; (either
10 across said terminals, whereby said circuit exhibits a nega
reverse breakdown voltage as in FIGURE 5 or constant
forward voltage as in FIGURE 6).
well de?ned at two switching points so as to cause the cur
tive resistance property whose V/I characteristic curve is
rent ?ow through the circuit to be approximately a linear
function of the voltage across said circuit.
2. A circuit according to claim 1 in which said ?rst end
For example, a desired 12 current of 1 ma; in FIGU
5 would require R(55) to be 1000 ohms, if the sum of
region of said ?rst device and said ?rst end region of said
the above-mentioned voltages across J3 and L; was l'volt.
A desired In current of 100m in FIGURE 6'would re
quire R(55) to be 6000 ohms if the sum of the above
mentioned voltages was 0.6 volt.
second device are of like conductivity material.
3. A circuit according to claim 1 in which said ?rst end
region of said ?rst device and said ?rst end region of said
What has beendescribed is an electrical circuit having 20 second device are of opposite conductivity material.
4. A circuit according to claim 1 in which said ?rst
a negative resistance characteristic whose changes in di
device consists of PNPN regions and has three rectifying
rection and slope ‘may be fully controlled, said circuit
comprising two semi-conductor devices in combination
junctions therein.
' V
5. A circuit according to claim 1 in which said second
device consists of PN regions and has one rectifying junc
tion therein;
6. A circuit according to claim 1 in which said‘ ?rst
with an external impedance so as to utilize the successive
voltage breakdown'of' a rectifying junction contained in
each for initiating current ampli?cation by one of said
Various modi?cations of the structure shown and de
device consists of PNPN regions having three rectifying
junctions therebetween, and said second device consists of
the spirit and ‘scope of'the invention, as now expressed in 30 PN regions having one rectifying junction therebetween.
7. A circuit according to claim 6 in which the end N
the-appended claims.’
region of said ?rst device is connected to the N region of
Whatis claimed is:
a said second device by said relatively low impedance means,
1. An electrical circuit comprising: a ?rst semi-conduc
and the inner P region of said ?rst device is connected to
tor device which can exhibit a negative‘resistance charac
the P region of said second device by said relatively high
teristic'having a plurality of regions of alternate conduc
scribed may obviously 'be made without departing from
tivity-type semi-conductor ‘material de?ning rectifying’
impedance means.
8. A circuit according to claim 6 in which the end N
region of said ?rst device is connected to the P region of
the two-terminal constant potential breakdown type, a
said second device by said relatively low impedance means,
relatively low impedance means connecting together a first
end region of said ?rst device with a ?rst end region of 40 and the inner P region of said ?rst device is connected to
junctions therebetween, a second semi-conductor device of
the'N region of said second device by said relatively high
said second device, a relatively high impedance means
connecting together second regions in said ?rst and second
impedance means.
devices, said second region in said ?rst device being adja
cent to said'?rst end region, a ?rst'rectifying junction in '
said ?rst device which offers a relatively high impedance
to'a voltage potential thereacross which is less than a'mag
nitude and whichbreaks down to o?er a'relatively low
impedance when said ?rst magnitude is reached, a ?rst .
rectifying junction in ‘said second device which offers a
relatively high impedance to a voltage potential there
across which is less than a second magnitude/and which
breaks‘ down to offer relatively low impedance when said ’
, References Cited in the ?le of this patent
Valdes ___-_'_ ________ __ Oct. 13, 1953
Shockley ____________ __ Oct; 13, 1953
2,735,948 .
_ 2,876,366
Ebers _______________ __ Oct. 13, 1953
Shockley __________ __V__ Aug. 30, 1955
Sziklai ______________ __ Feb. 21, 1956
Hussey ____' ___________ __ Mar. 3, 1959
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